Manganese oxide phases and morphologies: A study on calcination temperature and atmospheric dependence

Abstract

SummaryManganese oxides are one of the most important groups of materials in energy storage science. In order to fully leverage their application potential, precise control of their properties such as particle size, surface area and Mnx + oxidation state is required. Here, Mn3O4 and Mn5O8 nanoparticles as well as mesoporous α-Mn2O3 particles were synthesized by calcination of Mn(II) glycolate nanoparticles obtained through an economical route based on a polyol synthesis. The preparation of the different manganese oxides via one route facilitates assigning actual structure–property relationships. The oxidation process related to the different MnOx species was observed by in situ X-ray diffraction (XRD) measurements showing time- and temperature-dependent phase transformations occurring during oxidation of the Mn(II) glycolate precursor to α-Mn2O3 via Mn3O4 and Mn5O8 in O2 atmosphere. Detailed structural and morphological investigations using transmission electron microscopy (TEM) and powder XRD revealed the dependence of the lattice constants and particle sizes of the MnOx species on the calcination temperature and the presence of an oxidizing or neutral atmosphere. Furthermore, to demonstrate the application potential of the synthesized MnOx species, we studied their catalytic activity for the oxygen reduction reaction in aprotic media. Linear sweep voltammetry revealed the best performance for the mesoporous α-Mn2O3 species.

Study on Electrolyte Stability and Oxygen Reduction Reaction Mechanisms in the Presence of Manganese Oxide Catalysts for Aprotic Lithium–Oxygen Batteries

“…On the highly conductive, smooth glassy carbon (GC) surface and in the presence of the comparably large α‐Mn 2 O 3 catalyst particles ( d ≈0.5–2 μm), that is, on active surfaces with a rather low surface energy, diffusion‐controlled ORR processes that result in LiO 2 /Li 2 O 2 formation occurred (Scheme a). The electrode materials with smaller particle diameters and/or a lower electrical conductivity, commercial Vulcan® carbon powder (VC; d ≈0.8–9 μm), Mn 5 O 8 /C ( d (Mn 5 O 8 )≈20 nm), and Mn 3 O 4 /C ( d (Mn 3 O 4 )≈10 nm), were shown to promote diffusionless ORR processes with initial O ads formation and subsequent reduction reactions (Scheme b).…”

“…Catalyst synthesis : For the electrochemical measurements, the Mn x O y catalysts were used as synthesized, the synthesis of which has been described previously . In short, nanosized Mn II glycolate particles were synthesized as precursor material by a polyol process.…”

Effect of annealing and impurity concentration on the TL characteristics of nanocrystalline Mn-doped CaF2

“…This again could be explained on the basis of formation of the clusters of Mn 3 O 4 phase(s) (whereby some of the Mn 2þ ions get converted into Mn 3þ states or vice-versa, as discussed earlier, Mn 3 O 4 has a spinel structure wherein Mn could exist in 2þ as well as 3þ states) due to annealing and the diffusion of atmospheric oxygen at high temperature(s). Even if the oxidation does not take place the Mn(OH) 2 , as formed initially, could get decomposed to form MnO x during the temperature range 320e550 C and further higher order of more complex phases at higher temperatures (Augustin et al, 2015). The Mn-impurity thus could be in the 2þ as well as in 3þ or even in 4þ states but as it gets agglomerated to form clusters, i.e., the energy may be released non-radiatively.…”

Mechanistic study on the activity of manganese oxide catalysts for oxygen reduction reaction in an aprotic electrolyte

“…The obtained white powder was subsequently calcined in an Ar flow for 2 h at 350 C and at 550 C yielding Mn 3 O 4 and a-Mn 2 O 3 , respectively. Mn 5 O 8 was obtained by calcination of the precursor in an O 2 flow for 5 h at 400 C. The properties of the obtained MnO x particles are given in [23] and summarized in …”

“…The detailed synthesis of the MnO x catalysts are reported elsewhere [23]. In short, nanosized Mn II glycolate particles were synthesized as a precursor via a polyol process.…”